This is needed to produce a more unified ramdisk that can be
used for ansible-deploy with minimal rebuild
changes include:
- deprecate ENABLE_SSH var, split it to INSTALL_SSH and AUTHORIZE_SSH
 - INSTALL_SSH (defaults to true) installs and configures OpenSSH
 server
 - AUTHORIZE_SSH (defaults to false) adds SSH_PUBLIC_KEY as authorized
 for 'tc' user and makes some other changes
- symlink all from '/usr/local/(s)bin' to '/usr/(s)bin'
- adds a new script 'add-ssh-tinyipa' and 'addssh' make target
 - this effectively does those parts that finalise-tinyipa.sh script
 would do when AUTHORIZE_SSH is enabled
 - this make target will be used in gate jobs for ansible deploy
 interface
Change-Id: Ib6fcd5bbd7e79b9df83b660441dd685b1b17be62
Related-Bug: #1526308